Update chapter7.txt

Add the sequences for hidden and strike-through text

Author: sal666

manuscript/chapter7.txt

@@ -24,6 +24,8 @@ Contrary to popular belief, there is no issue in utilizing raw escape sequences.
 | `\e[4m` | Underline text. |
 | `\e[5m` | Slow blink. |
 | `\e[7m` | Swap foreground and background colors. |
+| `\e[8m` | Hidden text. |
+| `\e[9m` | Striket-hrough text. |
 
 
 ## Cursor Movement